GD::Graph lets you plot data point values above the point or bar. I've used that successfully with vertical bar charts.

gnuplot allows you to set labels and plot them on the graph. You can use the data for label text and the position. gnuplot can be used at the command prompt, from within a perl script, or with the Perl module Chart::Graph::Gnuplot. I think there would be serveral ways to get the label but not plot the data. Once to suppress part of the graph, I just set the point size to 0, gnuplot still generated all the axes, titles, lables, etc., just no points representing the data.